Adaptive self-tunable antenna system and method

ABSTRACT

Adaptive self-tunable antenna systems and methods are provided including a closed-loop system for sensing near-field RF signals of transmitted RF signals and tuning an antenna or switching between multiple antennas, so that the strength of the transmitted RF signals is maximized. A sensing antenna detects the near-field RF signal, which is filtered and converted to an RF strength control signal that can be used to generate an antenna tuning control signal. An antenna tuner uses the antenna tuning control signal to keep the antenna in resonance by dynamically changing the electrical length of the antenna or switching between multiple antennas to maximize the strength of the radiated RF signal. Such antennas may be less prone to detuning due to interaction with human bodies or other objects. Dynamically matching the antennas to an RF power amplifier and low noise amplifier can improve stability, power efficiency, gain, noise figure, and receiver sensitivity.

TECHNICAL FIELD

This application generally relates to adaptive self-tunable antennasystems and methods. In particular, this application relates to systemsand methods for adaptively tuning an antenna with a closed-loop systemincluding a sensing antenna, an RF detector, a processor, and an antennatuner; and for a tunable antenna.

BACKGROUND

Audio production can involve the use of many components, includingmicrophones, wireless audio transmitters, wireless audio receivers,recorders, and/or mixers for capturing and recording the sound ofproductions, such as television programs, newscasts, movies, liveevents, and other types of productions. The microphones typicallycapture the sound of the production, which is wirelessly transmittedfrom the microphones and/or the wireless audio transmitters to thewireless audio receivers. The wireless audio receivers can be connectedto a recorder and/or a mixer for recording and/or mixing the sound by acrew member, such as a production sound mixer. Electronic devices, suchas computers and smartphones, may be connected to the recorder and/ormixer to allow the crew member to monitor audio levels and timecodes.

Wireless audio transmitters, wireless audio receivers, and otherportable wireless communication devices include antennas fortransmitting radio frequency (RF) signals which contain digital oranalog signals, such as modulated audio signals, data signals, and/orcontrol signals. Users of portable wireless communication devicesinclude stage performers, singers, actors, news reporters, and the like.One common type of portable wireless communication device is a wirelessbodypack transmitter, which is typically secured on the body of a userwith belt clips, straps, tape, etc.

The electrically small antennas included on portable wirelesscommunication devices are typically low profile and small so that thesize of the devices is reduced, physical interaction with the antennasis minimized, and to assist in concealing the devices from an audience.Antennas may extend from the device or be included within the device,depending on the type of antenna being utilized. However, the usablebandwidth and efficiency of an antenna are reduced as the size of theantenna is reduced, due to fundamental physical limitations.Furthermore, electrically small antennas are more likely to be subjectto the detuning effects of being close to a human body. For example, anRF signal transmission may be degraded by 20 dB in some situationsbecause of the proximity of a human body near an antenna.

Typical antenna types used in portable wireless communication devicesinclude quarter wave whip antennas, partial or complete helicalantennas, ceramic chip antennas, and other types of antennas. Each ofthese antenna types has drawbacks. A quarter wave whip antenna mayextend from the device and therefore be excessively long, hard toconceal, and prone to damage. A partial or complete helical antenna mayalso extend from the device and have limited operating bandwidth,degraded radiation efficiency, and be prone to detuning when close to ahuman body. While able to be included within a device and physicallysmaller than the other antenna types, a ceramic chip antenna may havevery low radiation efficiency, extremely limited operating bandwidth,and also be prone to detuning when close to a human body.

Accordingly, there is an opportunity for systems and methods thataddress these concerns. More particularly, there is an opportunity foradaptive self-tunable antenna systems and methods for tuning an antennawith a closed-loop system for enabling the antenna to have increasedradiation resistance, improved radiation efficiency, maximized far fieldstrength for improved auto-tunable operating frequency, less sensitivityto detuning, and the ability to be integrated within a device.

SUMMARY

The invention is intended to solve the above-noted problems by providingan adaptive self-tunable antenna system and method that are designed to,among other things: (1) utilize a sensing antenna for detecting a nearfield radio frequency (RF) signal from an RF signal transmitted from anantenna; (2) convert the near field RF signal to an RF strength controlsignal based on the strength of the near field RF signal; (3) generatean antenna tuning control signal based on the RF strength controlsignal; (4) control an electrical length of the antenna with an antennatuner, based on the antenna tuning control signal, so that the strengthof the RF signal transmitted from the antenna is maximized; and (5)provide an electrically small antenna in communication with a tuningnetwork for improved radiation resistance and radiation efficiency. Theantenna may be an electronically tunable antenna, and may be have anytype of physical configuration.

In an embodiment, an adaptive self-tunable antenna system may include asensing antenna for detecting a near field RF signal of an RF signaltransmitted from a transmitting antenna. The system may also include aband pass filter for generating a filtered near field RF signal from thenear field RF signal, and an RF detector for converting the filterednear field RF signal to an RF strength control signal that represents astrength of the filtered near field RF signal. A processor may receivethe RF strength control signal and generate an antenna tuning controlsignal based on the RF strength control signal. An antenna tuner can beconfigured to control an electrical length of the transmitting antennabased on the antenna tuning control signal such that a strength of theRF signal transmitted by the transmitting antenna is maximized.

In another embodiment, a method for adaptively self tuning atransmitting antenna includes detecting a near field RF signal of an RFsignal transmitted from the transmitting antenna. The near field RFsignal may be band pass filtered to generate a filtered near field RFsignal. The filtered near field RF signal may be converted to an RFstrength control signal that represents a strength of the filtered nearfield RF signal, and an antenna tuning control signal may be generatedbased on the RF strength control signal. An electrical length of thetransmitting antenna may be controlled based on the antenna tuningcontrol signal, such that a strength of the RF signal transmitted by thetransmitting antenna is maximized.

In a further embodiment, an adaptive self-tunable antenna system mayinclude a sensing antenna for detecting a first near field RF signal ofa first RF signal at a first frequency, and for detecting a second nearfield RF signal of a second RF signal at a second frequency differentfrom the first frequency. The first RF signal may have been transmittedfrom a first transmitting antenna and the second RF signal may have beentransmitted from a second transmitting antenna. A first RF switch canconvey a selected near field RF signal from the first or second nearfield RF signals, based on whether the first or second RF signal isbeing transmitted. First and second band pass filters may generate firstand second filtered near field RF signals from the first and second nearfield RF signals, respectively. A second RF switch can convey a selectedfiltered near field RF signal from the first or second filtered nearfield RF signals, based on whether the first or second RF signal isbeing transmitted. An RF detector may convert the selected filtered nearfield RF signal to an RF strength control signal representing a strengthof the selected filtered near field RF signal. A processor may receivethe RF strength control signal and generate an antenna tuning controlsignal based on the RF strength control signal. A first antenna tunercan be configured to control an electrical length of the firsttransmitting antenna based on the antenna tuning control signal suchthat a strength of the first RF signal transmitted by the firsttransmitting antenna is maximized. A second antenna tuner can beconfigured to control an electrical length of the second transmittingantenna based on the tuning control signal such that a strength of thesecond RF signal transmitted by the second transmitting antenna ismaximized. In some embodiments, the second transmitting antenna mayinclude multiple transmitting antennas, such as in a diversityconfiguration, for example. In these embodiments, the second antennatuner can be configured to select the most efficient transmittingantenna at a given time instance for transmission of the RF signal.

In another embodiment, an antenna structure for transmitting an RFsignal includes a first helical branch and a second helical branchdisposed on a substrate. The first helical branch and the second helicalbranch are disposed parallel to one another, and are not electricallyconnected to one another. The antenna may also include a tuning networkin communication with the first and second helical branches, and beconfigured to control a first electrical length of the first helicalbranch and a second electrical length of the second helical branch suchthat a radiation resistance of the antenna is maximized. Each of thefirst and second helical branches of the antenna transmits the RFsignal.

These and other embodiments, and various permutations and aspects, willbecome apparent and be more fully understood from the following detaileddescription and accompanying drawings, which set forth illustrativeembodiments that are indicative of the various ways in which theprinciples of the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1B are block diagrams of a single-band adaptive self-tunableantenna system, in accordance with some embodiments.

FIGS. 2A-2B are block diagrams of a dual-band adaptive self-tunableantenna system, in accordance with some embodiments.

FIG. 3 is a flowchart illustrating operations for controlling anelectrical length of a transmitting antenna based on an RF strengthcontrol signal and an antenna tuning control signal using the system ofFIGS. 1A-1B, in accordance with some embodiments.

FIGS. 4A-4B are flowcharts illustrating operations for controllingelectrical lengths of transmitting antennas based on an RF strengthcontrol signal and an antenna tuning control signal using the systems ofFIGS. 2A-2B, respectively, in accordance with some embodiments.

FIG. 5 is a flowchart illustrating operations for generating an antennatuning control signal in conjunction with the operation of FIGS. 3 and4A-4B, in accordance with some embodiments.

FIG. 6 is an exemplary schematic of an antenna tuner, in accordance withsome embodiments.

FIG. 7 is an exemplary alternative schematic of an antenna tuner, inaccordance with some embodiments.

FIG. 8 show exemplary representations of antennas.

DETAILED DESCRIPTION

The description that follows describes, illustrates and exemplifies oneor more particular embodiments of the invention in accordance with itsprinciples. This description is not provided to limit the invention tothe embodiments described herein, but rather to explain and teach theprinciples of the invention in such a way to enable one of ordinaryskill in the art to understand these principles and, with thatunderstanding, be able to apply them to practice not only theembodiments described herein, but also other embodiments that may cometo mind in accordance with these principles. The scope of the inventionis intended to cover all such embodiments that may fall within the scopeof the appended claims, either literally or under the doctrine ofequivalents.

It should be noted that in the description and drawings, like orsubstantially similar elements may be labeled with the same referencenumerals. However, sometimes these elements may be labeled withdiffering numbers, such as, for example, in cases where such labelingfacilitates a more clear description. Additionally, the drawings setforth herein are not necessarily drawn to scale, and in some instancesproportions may have been exaggerated to more clearly depict certainfeatures. Such labeling and drawing practices do not necessarilyimplicate an underlying substantive purpose. As stated above, thespecification is intended to be taken as a whole and interpreted inaccordance with the principles of the invention as taught herein andunderstood to one of ordinary skill in the art.

The adaptive self-tunable antenna systems and methods described belowcan enable an antenna to have improved performance over other types ofantennas, and in particular, over electrically small conformal antennas.The closed-loop tuning of the systems and methods allowbandwidth-limited electrically small antennas to effectively have anoperative bandwidth approaching the bandwidth of quarter wave antennas,but be physically smaller and enclosed within a device, due to theconformal aspect of the antenna. Furthermore, the antenna has anincreased radiation resistance and improved radiation efficiency, andthe adaptive closed-loop antenna tuning system can dynamicallycompensate and minimize antenna detuning due to interaction with thehuman body or other interfering objects. In particular, the antennadetuning effects due to a human body, e.g., a person holding the device,may include altering conductor currents of the antenna, and can becompensated for with the adaptive self-tunable antenna systems andmethods.

FIG. 1A illustrates a block diagram of one embodiment of a single-bandadaptive self-tunable antenna system 100 for optimally transmitting aradio frequency (RF) signal. The system 100 may be a closed loop systemthat enables the antenna 102 to transmit the RF signal at a maximizedstrength and higher radiation efficiency through the use of a near fieldsensing antenna 104, a band pass filter 106, an RF detector 108, aprocessor 110, and an antenna tuner 112. By using the system 100, thebandwidth-limited tunable antenna 102 may transmit an RF signal at aparticular frequency, such as in the UHF/VHF band or other frequencyband, at maximum radiated power. The antenna 102 may include dualparallel helical branches, as described below, for example, or may be ofanother configuration. The RF signal transmitted by the antenna 102 maycontain audio signals or data signals modulated by analog and/or digitalmodulation schemes, for example. The signals may have been modulated byan analog or digital RF transceiver/transmitter 116 and amplified by aproperly matched power amplifier 114 (when RF transceiver/transmitter116 is in a transmitter configuration), or by a power amplifier/lownoise amplifier 114 (when RF transceiver/transmitter 116 is in atransceiver configuration). The RF transceiver/transmitter 116 may be incommunication with other components (not shown), such as a microphone orplayback device, with digital data signals, control signals, etc. Thesystem 100 may be included within a wireless audio transmitter, forexample, and the RF signal may be transmitted from the antenna 102 to bereceived by a wireless audio receiver, recorder, and/or other componentfor further processing.

The system 100 may also dynamically improve matching of the antenna 102to the output of the power amplifier 114. Such matching is typicallydegraded in the portable wireless system context due to variations inantenna impedance caused by interaction with a human body or otherobjects. As such, the self-tuning and matching enabled by the system 100can reduce design constraints for the power amplifier 114, improvestability and power efficiency, and reduce power consumption. Theoverall complexity and cost of components of the system 100, such as thepower amplifier 114 and/or RF transceiver/transmitter 116, may also bereduced compared to current systems.

The sensing antenna 104 may detect a near field RF signal of the RFsignal transmitted from the antenna 102. A radiative near field RFsignal is the RF signal that is physically closest to the antenna 102and is generally within a fraction of wavelength of the RF signal fromthe antenna. Detecting the near field RF signal with the sensing antenna104 enables the system 100 to determine the tuning of the antenna 102because there is a strong correlation between the strength of a nearfield RF signal and the strength of its associated far field RF signal.The far field RF signal is the RF signal that is the “real radiatedpower” signal that is received by a receiver situated farther away fromthe antenna. Accordingly, after sensing the near field RF signal, thesystem 100 can control the antenna tuner 112 to maximize the strength ofthe RF signal transmitted by the antenna 102. The sensing antenna 104may be a trace on a printed circuit board, a wire, or a broadbandantenna, for example, and may provide a high input impedance to the RFdetector 108 so that near field loading effects are minimized.

The near field RF signal may be provided from the sensing antenna 104 tothe band pass filter 106. The band pass filter 106 rejects RF signalsdetected by the sensing antenna 104 that are out of the frequency bandbeing transmitted by the antenna 102 in order to avoid antenna tuningdistortion. For example, if the sensing antenna 104 detects RF signalsat nearby frequencies from devices that are physically close to thesystem 100, the band pass filter 106 can filter out the other RF signalsso that the RF signal transmitted by the antenna 102 is furtherprocessed. The band pass filter 106 may be a discrete band pass filter,a microwave band pass filter, a SAW band pass filter, a helical bandpass filter, a dielectric band pass filter, or other type of filter. Theparticular type of band pass filter 106 may depend on out-of-bandrejection requirements. The RF detector 108 may convert the filterednear field RF signal from the band pass filter 106 to an RF strengthcontrol signal representing the strength of the filtered near field RFsignal. The RF strength control signal may be a DC voltage or a digitalsignal (e.g., SPI, I²C, etc.), for example. The RF detector 108 may becalibrated so that it is sensitive only to the minimum required dynamictuning range of the antenna 102, e.g., limited only to 5-15 dB. In thisway, interference caused by high power signals within the frequency bandcan be minimized. The RF detector 108 may be an AD8361 integratedcircuit from Analog Devices, Inc., for example.

The processor 110 may receive the RF strength control signal from the RFdetector 108 and generate an antenna tuning control signal based on theRF strength control signal. The processor 110 may be encompassed in thesystem 100 and perform other functionality, or may be a separatecomponent. Routines executing on the processor 110 may result in thetuning of the antenna 102 through generation of the antenna tuningcontrol signal to the antenna tuner 112. In particular, the antennatuner 102 may control the electrical length of the antenna 102 based onthe antenna tuning control signal so that the strength of thetransmitted RF signal is maximized. The processor 110 may periodicallysample the strengths of the near field RF signal at the currentfrequency, at the frequency one tuning state higher than the currentfrequency, and at the frequency one tuning state lower than the currentfrequency. The tuning control signal may then be generated so that theantenna 102 is tuned to the tuning state that has the highest measuredstrength of the near field RF signal. An embodiment of a method forgenerating the tuning control signal is described below with referenceto FIG. 5.

The antenna tuner 112 may be a balanced phase shifter that can controlthe electrical length of the antenna 102 based on the antenna tuningcontrol signal so that the strength of the transmitted RF signal ismaximized. In particular, the net reactance of the antenna tuner 112 canbe controlled using the antenna tuning control signal to tune theantenna 102 to have an antenna resonance at a particular frequency beingtransmitted. In one embodiment, shown in FIG. 6, the two branches of theantenna 601 are respectively connected to a tuning network 600 thatincludes an inductor 602 and a capacitor 604 connected in series. Theinductors 602 in the tuning network 600 may have a high quality factor Q(and a corresponding low series resistance value including thecapacitors 604) so that signal losses are minimized in the tuningnetwork 600. For antenna resonance at a low band edge frequency, thecapacitors 604 may be adjusted to a high value, e.g., 10-1000 pF,depending on the operating frequency in a particular band (e.g., VHF,UHF, L band, S band, C band, etc.), in conjunction with a properlyselected inductance of the inductors 602. The value of the capacitors604 can be decreased in order to move the antenna resonance to therequired operating frequency. The minimum value of the capacitors 604occur at a high band edge frequency of antenna resonance. FIG. 6 alsoincludes an embodiment with a single conductor helical antenna 603, aninductor 602, and a capacitor 604 connected in series. Use of theadaptive self-tuning system 100 can continuously compensate fordynamically changing loading effects on the antenna due to user handlingand proximity to a human body and other objects. The capacitors 604 maybe digitally tunable capacitors (DTC), microelectromechanical (MEMS)capacitors, or varactor diodes, for example. In particular, the tuningcontrol signal may control the capacitance values of the capacitors orvaractor diodes so that the electrical length of the antenna 601 isappropriately controlled.

In another embodiment, shown in FIG. 7, the two branches of the antenna102 are connected to a balanced tuning network 700 composed of PINdiodes. The PIN diodes can be used to short circuit or open circuitparticular segments in the tuning network 700, based on a tuning controlsignal presented to the network 700 on input ports 702. In particular,the appropriate PIN diodes may be biased so that the electrical lengthof the antenna 102 is controlled to cause the antenna 102 to resonate atthe desired frequency, based on the antenna tuning control signal. Theoperation of the balanced tuning network 700 has some similarities tothe tuning network 600 shown in FIG. 6. In some embodiments, the tuningcontrol signals for the PIN diodes on input ports 702 may be connectedto General Purpose Input/Output ports of a microcontroller or processor.In this configuration, the microcontroller or processor can turn on andoff the appropriate PIN diodes, based on an algorithm for generating theantenna tuning control signal. An antenna configuration including dualhelical branches may receive optimal benefits from the balanced tuningnetwork 700, while an antenna configuration including a single conductormay receive optimal benefits from the tuning network 600.

FIG. 1B illustrates a block diagram of another embodiment of asingle-band adaptive self-tunable antenna system 150 for optimallytransmitting a radio frequency (RF) signal. The system 150 may be aclosed loop system that enables the antennas 151, 152 to transmit the RFsignal at a maximized strength and higher radiation efficiency throughthe use of a near field sensing antenna 104, a band pass filter 106, anRF detector 108, a processor 110, and a RF switch 162. The antennas 151,152 may be fixed diversity antennas, and the RF switch 162 may selectthe best antenna of the antennas 151, 152 to transmit the RF signal. TheRF signal transmitted by the antennas 151, 152 may contain audio signalsor data signals modulated by analog and/or digital modulation schemes,for example. The near field sensing antenna 104, the band pass filter106, the RF detector 108, and the processor 110 in the system 150 mayeach have the same functionality as described above with respect to thesystem 100 of FIG. 1A. The processor 110 may also control the RF switch162 based on the antenna tuning control signal so, taking into accountthe antenna detuning effects of the human body, the particular antenna151, 152 that is radiating the highest power is selected fortransmission.

FIG. 2A illustrates a block diagram of a dual-band adaptive self-tunableantenna system 200 for optimally transmitting RF signals. The system 200may be a closed loop system that enables the antennas 202 and 252 totransmit RF signals at a maximized strength and higher radiationefficiency through the use of a sensing antenna 204, RF switches 205 and207, band pass filters 206 and 256, an RF detector 208, a processor 210,and antenna tuners 212 and 262. By using the system 200, the antenna 202may transmit an RF signal at a particular frequency, such as in a highfrequency band (e.g., 2.4 GHz or 5.7 GHz), and the antenna 252 maytransmit an RF signal at another frequency, such as in a low frequencyband (e.g., UHF/VHF), at maximum radiated power. In some embodiments,the antenna 202 may be tuned to transmit its RF signal during a preambleperiod of a digital transmission packet, and the antenna 252 may becontinuously tuned to transmit its RF signal (e.g., an analog modulationRF signal) except during the preamble period of the digital transmissionpacket being transmitted.

The antenna 202 may transmit RF signals in the high frequency band thatcontain monitoring and control signals, for example, that can enable themanagement of components within a larger system. The monitoring andcontrol signals may include adjustment of the gain of wireless audiotransmitters, monitoring of audio levels, and/or monitoring and controlof wireless aspects of the larger system, such as RF performance,statistics, etc. A wireless link (e.g., through an IEEE802.15.4/ZigBee-based protocol, such as ShowLink Remote Control,available from Shure Inc.) may be utilized for the monitoring andcontrol signals. The monitoring and control signals may have beengenerated by an RF transceiver/transmitter 216 and amplified by aproperly matched power amplifier 214 (when RF transceiver/transmitter216 is in a transmitter configuration), or by a power amplifier/lownoise amplifier 214 (when RF transceiver/transmitter 216 is in atransceiver configuration). The RF transceiver/transmitter 216 may be incommunication with other components (not shown). In some embodiments,the antenna 202 includes two chip antennas in a space diversityconfiguration when transmitting at 2.4 GHz. When transmitting at 2.4GHz, the sensing antenna 204 can monitor the strengths of the near fieldRF signals from both chip antennas during the preamble period of adigital transmission packet and then switch to the chip antenna that isradiating more RF power for the remaining duration of the digitaltransmission packet (e.g., the payload period).

The antenna 252 may include dual parallel helical branches, as describedbelow, for example, or may be of another configuration. The RF signaltransmitted by the antenna 252 may contain audio signals or data signalsmodulated by analog and/or digital modulation schemes, for example. Thesignals may have been modulated by an analog or digital RFtransceiver/transmitter 266 and amplified by a properly matched poweramplifier 264 (when RF transceiver/transmitter 266 is in a transmitterconfiguration), or by a power amplifier/low noise amplifier 264 (when RFtransceiver/transmitter 266 is in a transceiver configuration). The RFtransceiver/transmitter 266 may be in communication with othercomponents (not shown), such as a microphone or playback device, withdigital data signal, control signals, etc. The system 200 may beincluded within a wireless audio transmitter, for example, and the RFsignals may be transmitted by the antennas 202 and 252 to be received bya wireless audio receiver, recorder, and/or other component for furtherprocessing.

The sensing antenna 204 may detect near field RF signals of the RFsignals transmitted from the antennas 202 and 252. Detecting the nearfield RF signals with the sensing antenna 204 enables the system 200 todetermine the tuning of the antennas 202 and 252 because there is astrong correlation between the strength of a near field RF signal andthe strength of its associated far field RF signal. After sensing thenear field RF signals, the system 200 can control the antenna tuners 212and 262 to maximize the strengths of the RF signals transmitted by theantennas 202 and 252. The sensing antenna 204 may be a trace on aprinted circuit board, a wire, or a broadband antenna, for example, andmay provide a high input impedance to the RF detector 208 so that nearfield loading effects are minimized.

The detected near field RF signals may be provided from the sensingantenna 204 to an RF switch 205. The RF switch 205 may route thedetected near field RF signals to one of the band pass filters 206 and256, depending on a select signal that signifies whether the highfrequency band RF signal or the low frequency band RF signal is beingtransmitted. For example, if the preamble portion of a transmissionpacket in the high frequency band RF signal is being transmitted, the RFswitch 205 can route the near field RF signals to the high frequencyband band pass filter 206. If the preamble portion of the transmissionpacket in the high frequency band RF signal is not being transmitted,the RF switch 205 can route the near field RF signals to the lowfrequency band band pass filter 256. The select signal can be triggeredat the start of the preamble portion of the transmission packet, forexample.

The band pass filters 206 and 256 can each reject RF signals detected bythe sensing antenna 204 that are out of the frequency band beingtransmitted by the antennas 202 and 252, in order to avoid antennatuning distortion. For example, if the sensing antenna 204 detects RFsignals at nearby frequencies from devices that are physically close tothe system 200, the band pass filters 206 and 256 can filter out theother RF signals so that the RF signals transmitted by the antennas 202or 252 are further processed. In particular, since both the antennas 202and 252 can simultaneously transmit respective RF signals, the band passfilters 206 and 256 will respectively reject the RF signal that wastransmitted on the other frequency band, or other interfering signalsthat may be present. The band pass filters 206 and 256 may be a discreteband pass filter, a microwave band pass filter, a SAW band pass filter,a helical band pass filter, a dielectric band pass filter, or other typeof filter. The particular type of band pass filter 106 may depend onout-of-band rejection requirements.

The RF switches 205 and 207 can route the filtered near field RF signalsfrom the band pass filters 206 and 256 to the RF detector 208, dependingon the select signal. If the preamble portion of a transmission packetin the high frequency band RF signal is being transmitted, the RF switch207 can route the filtered near field RF signals from the high frequencyband band pass filter 206 to the RF detector 208. If the preambleportion of the transmission packet in the high frequency band RF signalis not being transmitted, the RF switch 207 can route the filtered nearfield RF signals from the low frequency band band pass filter 256 to theRF detector 208.

The RF detector 208 may convert the selected filtered near field RFsignal from the band pass filters 206 or 256 to an RF strength controlsignal representing the strength of the selected filtered near field RFsignal. The RF strength control signal may be a DC voltage or a digitalsignal (e.g., SPI, I²C, etc.), for example. The RF detector 208 may becalibrated so that it is sensitive to the minimum dynamic tuning rangerequired of the antennas 202 and 252, e.g., 15-25 dB. In this way,interference caused by high power signals within the frequency band canbe minimized. The RF detector 208 may be an AD8361 integrated circuitfrom Analog Devices, Inc., for example.

The processor 210 may receive the RF strength control signal from the RFdetector 208 and generate an antenna tuning control signal based on theRF strength control signal. The processor 210 may be encompassed in thesystem 200 and perform other functionality, or may be a separatecomponent. Routines executing on the processor 210 may result in thetuning of the antennas 202 and 252 through generation of the antennatuning control signal to the antenna tuners 212 or 262, depending onwhich antenna 202 or 252 is being tuned. In particular, the antennatuners 212 and 262 may control the electrical length of the antennas 202and 252, respectively, based on the antenna tuning control signal sothat the strengths of the transmitted RF signals are maximized. Theprocessor 210 may periodically sample the strengths of the near field RFsignals at the current frequency, at the frequency one tuning statehigher than the current frequency, and at the frequency one tuning statelower than the current frequency. The antenna tuning control signal maythen be generated so that the antenna 202 or 252 being tuned is tuned tothe tuning state that has the highest measured strength of the nearfield RF signal. An embodiment of a method for generating the tuningcontrol signal is described below with reference to FIG. 5.

The antenna tuner 262 may be a balanced phase shifter that can controlthe electrical length of the antenna 252 based on the antenna tuningcontrol signal so that the strength of the transmitted RF signal ismaximized. In particular, the net reactance of the antenna tuner 262 canbe controlled using the antenna tuning control signal to tune theantenna 252 to have an antenna resonance at the particular frequencybeing transmitted. As described above with reference to FIG. 1A, theremay be various embodiments of the antenna tuner 262, as described andshown in FIGS. 6 and 7.

FIG. 2B illustrates a block diagram of a dual-band adaptive self-tunableantenna system 270 for optimally transmitting RF signals. The system 270may be a closed loop system that enables the antennas 252 and 271, 272to transmit RF signals at a maximized strength and higher radiationefficiency through the use of a sensing antenna 204, RF switches 205 and207, band pass filters 206 and 256, an RF detector 208, a processor 210,antenna tuner 262, and an RF switch 282. The antennas 271, 272 maytransmit an RF signal at a particular frequency, such as in a highfrequency band (e.g., 2.4 GHz or 5.7 GHz). The antennas 271, 272 may befixed diversity antennas, and the RF switch 282 may select the bestantenna of the antennas 271, 272 to transmit the high frequency RFsignal. The RF signals transmitted by the antennas 271, 272 may containmonitoring and control signals, for example, that can enable themanagement of components within a larger system. The sensing antenna204, RF switches 205 and 207, band pass filters 206 and 256, RF detector208, processor 210, and antenna tuner 262 may each have the samefunctionality as described above with respect to the system 200 of FIG.2A. The processor 210 may also control the RF switch 282 based on theantenna tuning control signal so that the particular antenna 271, 272that is radiating the highest power is selected for transmission of thehigh frequency RF signal.

An embodiment of a process 300 for controlling an electrical length ofan antenna based on an antenna tuning control signal is shown in FIG. 3.The process 300 can result in the generation of an antenna tuningcontrol signal that controls the electrical length of an antenna so thatan RF signal is transmitted at a maximized strength and higher radiationefficiency. At step 302, an initial RF signal may be generated, such asby an RF transceiver or transmitter. The initial RF signal may containaudio or data signals modulated by analog and/or digital modulationschemes, for example. The initial RF signal may be amplified at step 304to an RF signal, such as with a power amplifier. The RF signal may betransmitted from an antenna at step 306 so that the RF signal can bereceived by a receiver component.

At step 308, a near field RF signal of the transmitted RF signal may bedetected, such as by a sensing antenna. A near field RF signal is the RFsignal that is physically closest to the antenna and is generally withina fraction of wavelength of the RF signal from the antenna. Detectingthe near field RF signal helps to determine the tuning of the antennabecause there is a strong correlation between the strength of a nearfield RF signal and the strength of its associated far field RF signal.The far field RF signal is the RF signal that is the “real radiatedpower” signal that is received by a receiver situated farther away fromthe antenna.

A filtered near field RF signal may be generated at step 310 from thenear field RF signal detected at step 308. The filtered near field RFsignal may be generated by a band pass filter, for example, so that RFsignals out of the frequency band being transmitted can be rejected. Atstep 312, the filtered near field RF signal may be converted to an RFstrength control signal, such as by an RF detector. The RF strengthcontrol signal may represent the strength of the filtered near field RFsignal and may be a DC voltage or a digital signal (e.g., SPI, I²C,etc.), for example. At step 314, an antenna tuning control signal may begenerated based on the RF strength control signal. The antenna tuningcontrol signal may be generated by routines executing on a processor,for example. The antenna tuning control signal may control an antennatuner at step 316 to control the electrical length of the transmittingantenna to maximize the strength of the transmitted RF signal. In someembodiments, at step 316, the antenna tuning control signal may controlan antenna tuner to select a best antenna for maximum radiated power,such as when the antenna being tuned has a multiple chip configuration.Further description of generating the antenna tuning control signal isdiscussed below with respect to FIG. 5.

Embodiments of processes 400 and 450 for controlling the electricallengths of antennas based on an antenna tuning control signal is shownin FIGS. 4A-4B, respectively. The processes 400 and 450 can result inthe generation of an antenna tuning control signal that controls theelectrical length of antennas transmitting at different frequencies sothat RF signals are transmitted at a maximized strength and higherradiation efficiency. The process 400 may be utilized in conjunctionwith the system 200 of FIG. 2A, and the process 450 may be utilized inconjunction with the system 270 of FIG. 2B, for example. By using theprocesses 400 and 450, one antenna may transmit an RF signal at aparticular frequency, such as in a high frequency band (e.g., 2.4 GHz),and another antenna may transmit an RF signal at another frequency, suchas in a low frequency band (e.g., UHF/VHF), at maximum radiated power.In some embodiments, the antenna transmitting the high frequency band RFsignal may be tuned to transmit its RF signal during a preamble periodof a digital transmission packet, and the antenna transmitting the lowfrequency band RF signal may be tuned to transmit its RF signal (e.g.,an analog modulation RF signal) except during the preamble period of thedigital transmission packet. In other embodiments, the low frequencyband antenna may transmit an RF signal that is a digital modulation RFsignal, and the high frequency band antenna may also transmit an RFsignal that is a digital modulation RF signal. In this case, the lowfrequency band RF signal may be tuned during a preamble period of itsdigital modulation RF signal that is synchronized with the preambleperiod of the digital modulation RF signal of the high frequency band RFsignal.

At step 402, an initial high frequency band RF signal may be generated,such as by an RF transceiver or transmitter. The initial high frequencyband RF signal may contain monitoring and control signals, for example.The initial high frequency band RF signal may be amplified at step 404to a high frequency band RF signal, such as with a power amplifier. Thehigh frequency band RF signal may be transmitted from an antenna at step406 so that the high frequency band RF signal can be received by areceiver component. At the same time or at a different time as steps 402to 406, an initial low frequency band RF signal may be generated at step408, such as by an RF transceiver or transmitter. The initial lowfrequency band RF signal may contain audio or data signals modulated byanalog and/or digital modulation schemes, for example. The initial lowfrequency band RF signal may be amplified at step 410 to a low frequencyband RF signal, such as with a power amplifier. The low frequency bandRF signal may be transmitted from an antenna at step 412 so that the lowfrequency band RF signal can be received by a receiver component.

At step 414, the near field RF signals of the transmitted high frequencyband RF signal and/or low frequency band RF signal may be detected by asensing antenna, for example. Detecting the near field RF signals helpsto determine the tuning of the antennas because there is a strongcorrelation between the strength of a near field RF signal and thestrength of its associated far field RF signal. At step 416, it may bedetermined whether the preamble portion of a digital transmission packetis being transmitted on the high frequency band RF signal. If thepreamble portion is being transmitted at step 416, then the processes400 and 450 continue to step 418. At step 418, a filtered high frequencyband near field RF signal may be generated from the high frequency bandnear field RF signal detected at step 414. The filtered high frequencyband near field RF signal may be generated by a high frequency band bandpass filter, for example, so that RF signals out of this frequency bandbeing transmitted can be rejected.

At step 420, the filtered high frequency band near field RF signal maybe converted to an RF strength control signal, such as by an RFdetector. The RF strength control signal may represent the strength ofthe filtered high frequency band near field RF signal and may be a DCvoltage or a digital signal (e.g., SPI, I²C, etc.), for example. At step422, an antenna tuning control signal may be generated based on the RFstrength control signal. The antenna tuning control signal may begenerated by routines executing on a processor, for example. In theprocess 400 shown in FIG. 4A, the antenna tuning control signal maycontrol an antenna tuner at step 424 to control the electrical length ofthe transmitting antenna to maximize the strength of the transmittedhigh frequency band RF signal. This can be accomplished by antennatuning, or by antenna selection if the high frequency band antenna has amultiple antenna configuration. Further description of generating thetuning control signal is discussed below with respect to FIG. 5. In theprocess 450 shown in FIG. 4B, following step 422, an RF switch may becontrolled by the antenna tuning control signal at step 454 so that thebest fixed antenna that is radiating the highest power during thepreamble portion is selected for transmission.

If the preamble portion of a digital transmission packet is not beingtransmitted on the high frequency band RF signal at step 416, then theprocesses 400 and 450 continue to step 426. At step 426, a filtered lowfrequency band near field RF signal may be generated from the lowfrequency band near field RF signal detected at step 414. The filteredlow frequency band near field RF signal may be generated by a lowfrequency band band pass filter, for example, so that RF signals out ofthis frequency band being transmitted can be rejected. At step 428, thefiltered low frequency band near field RF signal may be converted to anRF strength control signal, such as by an RF detector. The RF strengthcontrol signal may represent the strength of the filtered low frequencyband near field RF signal and may be a DC voltage or a digital signal(e.g., SPI, I²C, etc.), for example. At step 430, an antenna tuningcontrol signal may be generated based on the RF strength control signal.The antenna tuning control signal may be generated by routines executingon a processor, for example. The antenna tuning control signal maycontrol an antenna tuner at step 432 to control the electrical length ofthe transmitting antenna to maximize the strength of the transmitted lowfrequency band RF signal. Further description of generating the tuningcontrol signal is discussed below with respect to FIG. 5.

An embodiment of a process 500 for generating an antenna tuning controlsignal is shown in FIG. 5. The process 500 may be an embodiment of steps314, 422, and/or 430, as described above, for example. The antennatuning control signal may be generated based on the measured strength ofa detected near field RF signal so that a particular antenna is tuned tomaximize the strength of an RF signal transmitted by the antenna. Theprocess 500 may be performed by a processor, for example. At step 502, astrength of the near field RF signal at the current transmittedfrequency can be stored in a memory, for example. The strength of thenear field RF signal may be based on an RF strength control signalgenerated by an RF detector, as described above, for example. At step504, a first calibrating antenna tuning control signal may be generatedso that the antenna is tuned to a frequency one tuning state lower thanthe current frequency. An RF strength control signal signifying thestrength of a near field RF signal at this state may be received at step506. A first calibrating strength may be stored in a memory at step 508.The first calibrating strength may be based on the RF strength controlsignal received at step 506.

At step 510, a second calibrating antenna tuning control signal may begenerated so that the antenna is tuned to a frequency one tuning statehigher than the current frequency. An RF strength control signalsignifying the strength of a near field RF signal at this state may bereceived at step 512. A second calibrating strength may be stored in amemory at step 514. The second calibrating strength may be based on theRF strength control signal received at step 512. At step 516, theantenna tuning control signal may be generated so that the antenna istuned to the tuning state having the highest measured strength for thenear field RF signal. The strength stored at step 502, the firstcalibrating strength stored at step 508, and the second calibratingstrength stored at step 514 may be compared to one another to determinethe highest measured strength. The antenna calibration tuning statecorresponding to the highest measured near field strength (out of thethree tuning states) may then be tuned to at step 516. In this way, theantenna may be continuously adapted and self-tuned so that it istransmitting at the maximum power. The calibration state repetitionperiods and step sizes may be configured and optimized depending on theparticular protocols of the wireless system and the propagation profile.

FIG. 8 illustrates exemplary representations of antennas, includingantennas with dual helical branches. The antennas shown in FIG. 8 cantransmit an RF signal that contains audio or data signals modulated byanalog and/or digital modulation schemes, for example. The signals mayhave been modulated by an RF transceiver/transmitter and amplified by apower amplifier, in some embodiments. The RF transceiver/transmitter maybe in communication with other components (not shown), such as amicrophone or playback device, with digital data signals, controlsignals, etc. The antennas shown in FIG. 8 are exemplary embodiments ofan antenna that could be used in the systems 100 and 200 describedabove. A ground plane of the antennas may include electronic andmechanical components of the device (e.g., printed circuit board coppergrounding, RF shielding, battery, etc.), and/or a person holding thedevice, for example.

The antennas 802, 804, 806, 808, 810, and 812 shown in FIG. 8 mayinclude dual helical branches. The helical branches may be conforminglyconstructed on a substrate, such as on a plastic enclosure of a device,e.g., a wireless audio transmitter or other portable wirelesscommunications device. Laser direct structuring on injection moldedplastic parts may be utilized to print the helical branches on theplastic enclosure, for example. In this way, the antennas 802, 804, 806,808, 810, and 812 may be integrated within the device and be protectedfrom potential damage due to physical interaction with a user or otherobjects.

The helical branches may be composed of conductors, such as wires orplated conductors. In FIG. 8, a portion of each of the antennas 802,804, 806, 808, 810, and 812 is shown in a three dimensional view, and across section of each of the antennas is also shown to the left of eachantenna to show the spatial positioning of the conductors. Inparticular, the antennas 802 and 804 show that the helical branchesinclude a conductor strip and a wire. The wires in the antennas 802 and804 are in a bottom orientation and a middle orientation, respectively.The antennas 806 and 808 show that the helical branches include a wideconductor strip and a narrower conductor strip. The narrower conductorstrip in the antennas 806 and 808 are in a bottom orientation and amiddle orientation, respectively. The antenna 810 shows that the helicalbranches include two conductor strips. The antenna 812 shows that thehelical branches include two wires. The helical branches are notelectrically connected to one another, and may have different geometriesand/or physical lengths.

The antennas 814 and 816 include a three-dimensional single spiral thatmay be a conductor strip or a wire. In the antenna 814, a single portfeed may be included for receiving or transmitting of the RF signalbeing fed to Port 1. A dual port feed may be included for receiving ortransmitting the RF signal being fed to Port 2 with Port 1 connected toground, as shown in the antenna 816. The antennas 814 and 816 may beconformingly constructed on a substrate, such as on a plastic enclosureof a device and have different shapes and form factors. The antennas 814and 816 may be integrated within the device and be protected frompotential damage due to physical interaction with a user or otherobjects.

An antenna or each of the branches of an antenna can be connected to atuning network that tunes the antenna to resonance and improves theradiation efficiency of the antenna. The tuning network may includeinductors, digitally tunable capacitors, microelectromechanical (MEMS)capacitors, and/or PIN diodes, as described above, to allow the tuningof the antenna to control its electrical length and maximize thetransmission strength of an RF signal.

This disclosure is intended to explain how to fashion and use variousembodiments in accordance with the technology rather than to limit thetrue, intended, and fair scope and spirit thereof. The foregoingdescription is not intended to be exhaustive or to be limited to theprecise forms disclosed. Modifications or variations are possible inlight of the above teachings. The embodiment(s) were chosen anddescribed to provide the best illustration of the principle of thedescribed technology and its practical application, and to enable one ofordinary skill in the art to utilize the technology in variousembodiments and with various modifications as are suited to theparticular use contemplated. All such modifications and variations arewithin the scope of the embodiments as determined by the appendedclaims, as may be amended during the pendency of this application forpatent, and all equivalents thereof, when interpreted in accordance withthe breadth to which they are fairly, legally and equitably entitled.

The invention claimed is:
 1. An adaptive self-tunable antenna system,comprising: a sensing antenna for detecting a near field radio frequency(RF) signal of an RF signal transmitted from a transmitting antenna, theRF signal comprising one or more of an analog modulated signal or adigital modulated signal; a band pass filter in communication with thesensing antenna, the band pass filter for generating a filtered nearfield RF signal from the near field RF signal; an RF detector incommunication with the band pass filter, the RF detector for detecting apower of the filtered near field RF signal and outputting an RF strengthcontrol signal representing a strength of the filtered near field RFsignal; and a processor in communication with the RF detector, theprocessor configured to receive the RF strength control signal andgenerate an antenna tuning control signal based on the RF strengthcontrol signal, wherein the antenna tuning control signal is forcontrolling an electrical length of the transmitting antenna such that astrength of the RF signal transmitted by the transmitting antenna ismaximized, wherein the processor is configured to generate the antennatuning control signal by: storing the strength of the RF signal at acurrent frequency, based on the RF strength control signal; generating afirst calibrating antenna tuning control signal such that thetransmitting antenna is tuned to a first frequency one tuning statelower than the current frequency of the RF signal; receiving the RFstrength control signal; storing a first calibrating strength of the RFsignal based on the RF strength control signal; generating a secondcalibrating tuning control signal such that the transmitting antenna istuned to a second frequency that is one tuning state higher than thecurrent frequency of the RF signal; receiving the RF strength controlsignal; storing a second calibrating strength of the RF signal based onthe RF strength control signal; and generating the antenna tuningcontrol signal such that the transmitting antenna is tuned to aresonance at one of the first frequency, the second frequency, or thecurrent frequency based on the greater of the first calibratingstrength, the second calibrating strength, and the strength of the RFsignal.
 2. The adaptive self-tunable antenna system of claim 1, furthercomprising: the transmitting antenna for transmitting the RF signal; anantenna tuner in communication with the processor and the transmittingantenna, the antenna tuner configured to control the electrical lengthof the transmitting antenna based on the antenna tuning control signal;an RF transmitter for generating an initial RF signal comprising the oneor more of the analog modulated signal or the digital modulated signal;and an RF power amplifier in communication with the RF transmitter andthe antenna tuner, the RF power amplifier for amplifying the initial RFsignal to the RF signal and transmitting the RF signal to the antennatuner.
 3. The adaptive self-tunable antenna system of claim 2, whereinthe antenna tuner comprises a phase shifter.
 4. The adaptiveself-tunable antenna system of claim 3, wherein: the phase shiftercomprises at least one inductor in series with at least one capacitorand the transmitting antenna; and a capacitance value of the at leastone capacitor is selected based on the antenna tuning control signal,wherein the selected capacitance value controls the electrical length ofthe transmitting antenna.
 5. The adaptive self-tunable antenna system ofclaim 4, wherein the at least one capacitor comprises one or more of atleast one digitally tunable capacitor or at least onemicroelectromechanical capacitor.
 6. The adaptive self-tunable antennasystem of claim 3, wherein: the phase shifter comprises at least oneinductor in series with at least one varactor diode and the transmittingantenna; and a capacitance value of the at least one varactor diode isdetermined based on the antenna tuning control signal, wherein theselected capacitance value controls the electrical length of thetransmitting antenna.
 7. The adaptive self-tunable antenna system ofclaim 3, wherein: the phase shifter comprises at least one PIN diode incommunication with the transmitting antenna; and the at least one PINdiode is biased based on the antenna tuning control signal, wherein thebiasing of the at least one PIN diode controls the electrical length ofthe transmitting antenna.
 8. The adaptive self-tunable antenna system ofclaim 3, wherein the phase shifter comprises one or more of a balancedphase shifter or a single ended phase shifter.
 9. The adaptiveself-tunable antenna system of claim 2, wherein the transmitting antennacomprises a first helical branch and a second helical branch, the firsthelical branch and the second helical branch disposed parallel to oneanother and not electrically connected to one another.
 10. The adaptiveself-tunable antenna system of claim 9, wherein: the first helicalbranch has a first length; and the second helical branch has a secondlength different from the first length.
 11. The adaptive self-tunableantenna system of claim 9, wherein: the first helical branch has a firstgeometry; and the second helical branch has a second geometry differentfrom the first geometry.
 12. The adaptive self-tunable antenna system ofclaim 2, wherein the transmitting antenna comprises a single helicalbranch.
 13. The adaptive self-tunable antenna system of claim 1, whereinthe sensing antenna comprises one or more of a trace on a printedcircuit board or a broadband antenna.
 14. The adaptive self-tunableantenna system of claim 1, wherein the RF signal contains one or more ofan audio signal or a data signal.
 15. A method for adaptivelyself-tuning a transmitting antenna, comprising: detecting a near fieldradio frequency (RF) signal of an RF signal transmitted from thetransmitting antenna, the RF signal comprising one or more of an analogmodulated signal or a digital modulated signal; band pass filtering thenear field RF signal to generate a filtered near field RF signal fromthe near field RF signal; detecting a power of the filtered near fieldRF signal and outputting an RF strength control signal representing astrength of the filtered near field RF signal; and generating an antennatuning control signal based on the RF strength control signal, whereinthe antenna tuning control signal is for controlling an electricallength of the transmitting antenna such that a strength of the RF signaltransmitted by the transmitting antenna is maximized, wherein generatingthe antenna tuning control signal comprises: storing the strength of theRF signal at a current frequency, based on the RF strength controlsignal; generating a first calibrating antenna tuning control signalsuch that the transmitting antenna is tuned to a first frequency onetuning state lower than the current frequency of the RF signal;receiving the RF strength control signal; storing a first calibratingstrength of the RF signal based on the RF strength control signal;generating a second calibrating tuning control signal such that thetransmitting antenna is tuned to a second frequency that is one tuningstate higher than the current frequency of the RF signal; receiving theRF strength control signal; storing a second calibrating strength of theRF signal based on the RF strength control signal; and generating theantenna tuning control signal such that the transmitting antenna istuned to a resonance at one of the first frequency, the secondfrequency, or the current frequency based on the greater of the firstcalibrating strength, the second calibrating strength, and the strengthof the RF signal.
 16. The method of claim 15, further comprising:generating an initial RF signal comprising the one or more of the analogmodulated signal or the digital modulated signal; amplifying the initialRF signal to the RF signal; transmitting the RF signal from thetransmitting antenna; and controlling the electrical length of thetransmitting antenna based on the antenna tuning control signal.
 17. Themethod of claim 16, wherein controlling the electrical length of thetransmitting antenna comprises selecting a capacitance value of at leastone capacitor based on the antenna tuning control signal, wherein theselected capacitance value controls the electrical length of thetransmitting antenna and the at least one capacitor is in series with atleast one inductor and the transmitting antenna.
 18. The method of claim17, wherein the at least one capacitor comprises one or more of at leastone digitally tunable capacitor or at least one microelectromechanicalcapacitor.
 19. The method of claim 16, wherein controlling theelectrical length of the transmitting antenna comprises determining acapacitance value of at least one varactor diode based on the antennatuning control signal, wherein the selected capacitance value controlsthe electrical length of the transmitting antenna and the at least onevaractor diode is in series with at least one inductor and thetransmitting antenna.
 20. The method of claim 16, wherein controllingthe electrical length of the transmitting antenna comprises biasing atleast one PIN diode based on the antenna tuning control signal, whereinthe biasing of the at least one PIN diode controls the electrical lengthof the transmitting antenna and the at least one PIN diode is incommunication with the transmitting antenna.
 21. The method of claim 15,wherein the transmitting antenna comprises a first helical branch and asecond helical branch, the first helical branch and the second helicalbranch disposed parallel to one another and not electrically connectedto one another.
 22. The method of claim 21, wherein: the first helicalbranch has a first length; and the second helical branch has a secondlength different from the first length.
 23. The method of claim 21,wherein: the first helical branch has a first geometry; and the secondhelical branch has a second geometry different from the first geometry.24. The method of claim 15, wherein the transmitting antenna comprises asingle helical branch.
 25. An adaptive self-tunable antenna system,comprising: a sensing antenna for detecting a first near field radiofrequency (RF) signal of a first RF signal transmitted from a firsttransmitting antenna, and a second near field RF signal of a second RFsignal transmitted from a second transmitting antenna, wherein the firstRF signal is a first frequency and the second RF signal is at a secondfrequency different from the first frequency; a first RF switch incommunication with the sensing antenna, the first RF switch forconveying a selected near field RF signal from the first near field RFsignal or the second near field RF signal, based on whether the first RFsignal or the second RF signal is to be transmitted; a first band passfilter in communication with the first RF switch, the first band passfilter for generating a first filtered near field RF signal from thefirst near field RF signal; a second band pass filter in communicationwith the first RF switch, the second band pass filter for generating asecond filtered near field RF signal from the second near field RFsignal; a second RF switch in communication with the first and secondband pass filters, the second RF switch for conveying a selectedfiltered near field RF signal from the first filtered near field RFsignal or the second filtered near field RF signal, based on whether thefirst RF signal or the second RF signal is to be transmitted; an RFdetector in communication with the second RF switch, the RF detector fordetecting a power of the selected filtered near field RF signal andoutputting a RF strength control signal representing a strength of theselected filtered near field RF signal; and a processor in communicationwith the RF detector, the processor configured to receive the RFstrength control signal and generate an antenna tuning control signalbased on the RF strength control signal, wherein the antenna tuningcontrol signal is for controlling a respective electrical length of thefirst or second transmitting antenna such that a strength of the firstor second RF signal transmitted by the first or second transmittingantenna is maximized, wherein the processor is configured to generatethe antenna tuning control signal by: storing the strength of atransmitted RF signal at a current frequency, based on the RF strengthcontrol signal, wherein the transmitted RF signal comprises: (1) thefirst RF signal if the first RF signal is to be transmitted or (2) thesecond RF signal if the second RF signal is to be transmitted;generating a first calibrating antenna tuning control signal such that atransmitting antenna is tuned to a first frequency one tuning statelower than the current frequency of the transmitted RF signal, whereinthe transmitting antenna comprises (1) the first transmitting antenna ifthe first RF signal is to be transmitted or (2) the second transmittingantenna if the second RF signal is to be transmitted; receiving the RFstrength control signal; storing a first calibrating strength of thetransmitted RF signal based on the RF strength control signal;generating a second calibrating tuning control signal such that thetransmitting antenna is tuned to a second frequency that is one tuningstate higher than the current frequency of the transmitted RF signal;receiving the RF strength control signal; storing a second calibratingstrength of the transmitted RF signal based on the RF strength controlsignal; and generating the antenna tuning control signal such that thetransmitting antenna is tuned to a resonance at one of the firstfrequency, the second frequency, or the current frequency based on thegreater of the first calibrating strength, the second calibratingstrength, and the strength of the transmitted RF signal.
 26. Theadaptive self-tunable antenna system of claim 25, further comprising: afirst antenna tuner in communication with the processor and the firsttransmitting antenna, the first antenna tuner configured to control thefirst electrical length of the first transmitting antenna based on theantenna tuning control signal; and a second antenna tuner incommunication with the processor and the second transmitting antenna,the second antenna tuner configured to control the second electricallength of the second transmitting antenna based on the antenna tuningcontrol signal.
 27. The adaptive self-tunable antenna system of claim25, wherein: the first frequency is in a high frequency band; the firstRF signal is a first digital modulated signal; the second frequency isin a low frequency band; and the second RF signal is one or more of ananalog modulated signal or a second digital modulated signal.
 28. Theadaptive self-tunable antenna system of claim 27, wherein: if a preambleof the first digital modulated signal is being transmitted: the selectednear field RF signal conveyed by the first RF switch is the first nearfield RF signal; and the selected filtered near field RF signal conveyedby the second RF switch is the first filtered near field RF signal; andif the preamble of the first digital modulated signal is not beingtransmitted: the selected near field RF signal conveyed by the first RFswitch is the second near field RF signal; and the selected filterednear field RF signal conveyed by the second RF switch is the secondfiltered near field RF signal.